This invention relates to alarm apparatus, and more particularly, to an alarm apparatus which detects the presence of a signal to maintain the apparatus in a non-alarm condition. When the signal is absent, the alarm apparatus is operable to detect the absence of the signal and go into alarm.
Still more particularly, the alarm apparatus of the invention includes a loop of wire placed around an area to be guarded and electrical circuitry is connected with the wire loop for detecting signals imposed on the loop. A child or the like within the area bounded by the wire is provided with a sending unit or transmitter which imposes a signal on the loop so long as the child remains within the area bounded by the loop, and the alarm circuitry thus remains in a non-alarm condition. However, in the event the child or the like goes beyond the area bounded by the loop, the transmitter worn by him no longer imposes a signal on the loop, with the result that the alarm circuitry enters an alarm condition.
The advantages of such an alarm apparatus are apparent. Children like to explore and child psychologists believe that exploration is important to a child's natural development. However, since a child is generally naive about the dangers in his environment, it is not generally regarded safe to permit a child to explore without close supervision. Since close supervision is not always convenient or possible, small children are placed in playpens and other confinements. If these confinements are used excessively, they can hinder healthy development of the child. The present invention solves parents' dilemma of how to let their children play in the open without having to constantly be watched.